Photographic silver halide emulsions containing 1-thia-3, 5, 7-triazaindenes



United States Patent PHOTOGRAPHIC SILVER HALIDE EMULSIONS CONTAINING1-'IH1A-3,5,7-TRIAZA1NDENES Charles F. H. Allen and John J. Sagura,Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y.,a corporation of New Jersey No Drawing. Application January 3, 1955,Serial No. 479,683

6 Claims. (Cl. 96-109) This invention relates to fog inhibiting agentsand stabilizers for photographic emulsions and to photographic emulsionscontaining them.

It is .well known that photographic emulsions on storage tend to losesensitivity and to become spontaneously developable Without exposure tolight. There is normally a detectable amount of the silver salt reducedduring development in the areas where no exposure was given; this iscommonly called fog, and sometimes called chemical fog where it isnecessary to distinguish between it and the eflects of accidentalexposure to radiation; in this invention, we are not concerned with thelatter.

Fog depends both on the emulsion and the conditions of development; fora given emulsion it increases with the degree of development. Withconstant development conditions, it tends to increase with time,temperature and relative humidity of storage conditions; it is commonpractice to make accelerated tests of the stability of photographicemulsions by storage at increased temperature or humidity, or both. Itis, of course, desirable to have emulsions as stable as possible underthe condi tions of high temperature and humidity which may occur intropical climates, for example. Fog usually appears over the whole areaof the sensitive coating, but when severe, it frequently is non-uniform.Fog may also be caused by exposure to chemicals, for example, hydrogensulfide and other reactive sulfur compounds, hydrogen peroxide vapor,and strongly reducing materials. While antifoggants and stabilizers mayprotect, to some extent, against such effects, it is normally understoodthat an antifoggant protects against spontaneous growth of fog duringprolonged storage or storage at high temperatures and humidities, orduring development to maximum contrast and speed, or both.

According to our invention we provide a method for stabilizingphotographic silver halide emulsions by incorporating therein a compoundselected from those represented by the following general formula:

(I) h s Kai l wherein R represents an alkylmercapto group, such asmethylmercapto, ethylmercapto, carboxyrnethylmercapto,carbomethoxymethylmercapto, etc. (e. g., an alkylmercapto groupcontaining from 1 to 3 carbon atoms) or a monoalkylamino group, such asmethylarnino, ethylamino, etc. (e. g., a monoalkylamino group containingfrom 1 to 2 carbon atoms), and R1 represents a hydrogen atom or a loweralkyl group, such as methyl, ethyl, etc. (e. g., an alkyl group of theformula CnH21L+1 wherein n is a positive integer of from 1 to 2) Thecompounds represented by Formula I above can advantageously be preparedaccording to the method described by Cook et al.

2,772,164 Patented Nov. 27, 1956 ice Jour. Chem. Soc. (1949), pages 1064and 2329. The compounds selected from those represented by Formula Iabove can alternatively be written according to the following generalformula:

It is, therefore, an object of the present invention to provide a methodfor stabilizing photographic emulsions. A further object is to provide ameans for reducing the fog produced upon keeping of such emulsions whichhave been sensitized, especially emulsions stored under tropical orother adverse conditions. A still further object is to provide a meansfor stabilizing the speed and contrast of sensitized photographicemulsions. Other objects will become apparent from a consideration ofthe following description and examples.

The antifoggant compounds represented by Formula I (or Ia) can beemployed in emulsions which have been sensitized optically orchemically, or emulsions which have not been so sensitized. It is knownthat the effective sensitivity of photographic silver halide emulsionscan be increased by adding to them derivatives of alkylene oxides, suchas ethylene oxide polymers having molecular weights of 300 or more. Thepractical value of these compounds is severely limited by their tendencyto increase fog on storage of the photographic film, especially storageat elevated temperatures and humidity. It has been found difiicult tocontrol this by the antifoggants commonly available without usingquantities of antifoggant which partly neutralize the speed increaseobtained from the alkylene oxide derivatives.

The alkylene oxide polymers used to sensitize the emulsions can be ofvarious types. The alkylene oxides from which the polymers are derivedcontain from 2 to 4 carbon atoms, e. g., ethylene oxide, propylene oxideand butylene oxide. The preparation of polymers from these compounds isdescribed in Ellis, The Chemistry of Synthetic Resins (1935), pages 990to 994. These compounds are also referred to as polyalkylene glycols andtheir use as sensitizers for silver halide emulsions is described in U.S. Patents 2,423,549 and 2,441,389. Ethylene oxide polymers have beenfound to be especially advantageous in practicing our invention.

Various derivatives of alkylene oxides may also be used to sensitize thesilver halide emulsions, e. g., condensation products of alkylene oxidewith glycols, such as those having from 8 to 18 carbon atoms, asdescribed in U. S. Patent 2,240,472 and British Patent 443,559, as wellas condensation products of alkylene oxides with aliphatic alcohols,aliphatic acids and aliphatic amines, that is, polyalkylene ethers,esters and amides, the preparation of which is described in U. S. Patent1,970,578, condensation products of alkylene oxides with phenols, alsodescribed in U. S. Patent 1,970,578, and condensation products ofalkylene oxides with hexitol ring dehydration products, as described inU. S. Patent 2,400,532.

In each case the polyalkylene oxide or derivative of alkylene oxideshould have a molecular weight of at least 300. Condensation products ofethylene oxide with long chain alcohols should have a molecular weightof about 700; other derivatives may have a molecular weight of 1500 to4000 or more.

The principal purpose of our invention is to provide a means formaintaining the sensitivity and fog of silver halide emulsions at orclose to initial optimum values under conditions of high temperature orhigh humidity, or both. Preferably, the antifoggants of our inventionare added to the emulsion at any stage during the process of manufactureprior to coating the emulsion, The antifoggants can be added to theemulsion in solution in any convenient solvent not injurious to theemulsion, such as lower aliphatic alcohols.

. The solutions of antifoggants which we employ when added in suitableconcentration before coating to unsen sitized or optically sensitizedsilver halide emulsions usually do not appreciably affect thesensitivity and fog when measurements are made soon after coating.However, when sensitometric measurements are made after appreciableintervals of time under tropical or dry con ditions of storage atelevated temperatures, the antifoggants do stabilize speed and maintainfog at a low level.

The alkylene oxide derivatives which can be used to sensitize theemulsions can be illustrated by the following specific examples,although our invention is in no Way limited to the use of these specificcompounds.

H OH CHZO (CHZCHZO)I|OH2CHZOH Polyethylene oxide O(CH2CH2O)nCH2CHzOH O(CH2CH20) nOHZCHflOH Di- (polyethylene-glycoxy) -decane HO CHzCHgO(CH2CH2O)71CH2OH1O 0 711 Polyethylene oxide oleyl ether where n=aninteger greater than about 10.

The preparation of silver halide emulsions involves three separateoperations: (1) the emulsification and digestion or ripening of thesilver halide, (2) the freeing of'the emulsion from aqueous solublesalts usually by washing, (3) the second digestion or after-ripening toobtain increased sensitivity (Mees, The Theory of the PhotographicProcess, 1942, page 3). The fog inhibiting agents can be added at anystage, preferably after the final digestion.

The photographic emulsions which we use are of the developing-out typeand best results have been obtained with gelatino-silver bromoiodideemulsions. However, emulsions of varying halide content can be. used.

The emulsions can be chemically sensitized by any of the acceptedprocedures. The emulsions can be digested with naturally active gelatin,or sulfur compounds may be added such as those described in Sheppard U.S. Patents 1,574,944 and U. S. 1,623,499, and Sheppard and Brigham U. S.Patent 2,410,689.

The emulsions can also be treated with salts of the noble metals such asruthenium, rhodium, palladium, iridium and platinum, all of which belongto group VIII of the periodic table of elements and have an atomicweight greater than 100, Representative compounds are ammoniumchloropalladate, potassium chloroplatinate and sodium chloropalladite,which are used for sensitizing in amounts below that which produces anysubstantial fog inhibition, as described in Smith and Trivelli U. S.Patent 2,448,060, and as antifoggants in higher amounts, :as describedin Trivelli and Smith U. S. Patents 2,566,245 and 2,566,263.

The emulsions can also be chemically sensitized with gold salts asdescribed in Waller and Dodd U. S. Patent 2,399,083, or stabilized withgold salts as described in Damschroder U. S. Patent 2,597,856 and Yutzyand Leermakers U. S. Patent 2,597,915. Suitable compounds are potassiumchloroaurite, potassium aurithiocyanate, potassium chloroaurate, aurictrichloride and 2-aurosulfobenzothia'zole methochloride.

The emulsions can also be chemically sensitized with reducing agents,such as stannous salts (Carroll U. S. Patent 2,487,850), polyamines suchas diethylene triamine (Lowe and Jones U. S. Patent 2,518,698),polyamines such as spermine (Lowe and Allen U, S. Patent 2,521,925), orbis-(fi-aminoethyl) sulfide and its watersoluble salts (Lowe and JonesU. S. Patent 2,521,926).

The emulsions can also be stabilized with the mercury compounds ofAllen, Byers and Murray, U. S. application Serial No. 319,611 (now U. S.Patent 2,728,663,-issued December 27, 1955), Carroll and Murray U. S.application Serial No. 319,612 (now U S. Patent 2,728,664, issuedDecember 27, 1955) and Leubner and Murray U. S. application Serial No.319,613 (now U. S. Patent 2,728,665, issued December 27, 1955), allfiled Novemnor 8, 1952.

The antifoggants of our invention alone, or in combination withpolyalkylene oxides or their derivatives, are

effective in the presence or absence of optical sensitizing dyes. Sinceoptical sensitizing can affect stability of emulsions with respect tosensitivity, fog and latent image changes, the action of theantifoggants is not completely independent or" optical sensitizing orother emulsion variables. We have found, however, that both unsensitizedemulsions and emulsions sensitized with cyanine or merocyanine dyes, orboth, can be treated with the antifoggant compounds represented byFormula I (or Ia) above.

The quantity of antifoggant compound employed can be varied, dependingupon the particular silver halide employed, degree of ripening, presenceor absence of other emulsion addenda, etc. In general, the quantity ofantifoggant can vary from about 0.005 to 0.25 gram per gram mole ofsilver halide in the emulsion. amounts can be used in combination withone or more of the chemical sensitizing and stabilizing agents listedabove.

The stabilizing action afforded by the antifoggants'of our invention wasdetermined by incubation of the emulsions for a period of one week at F.and at constant humidity. The speeds were-measured in terms of 30/Ewhere E is the exposure required to produce a density of 0.2 above fog.The antifogg-ants were added to a panchromatically sensitized, highspeed silver bromiodide emulsion which had been chemically sensitizedwith a sulfur compound, such as described in Sheppard U. S'Patent1,574,944 and potassium chloroaurate. The emulsions were coated on acellulose acetate support and the coatings exposed on an Eastman I(b)sensitometer and processed for five minutes in a developer having thefollowing composition:

Grams N-methyl-p-aminophenol sulfate 2.5 Hydroquinone 1.3 Sodium sulfite(desiccated) 30.0 Sodium metaborate 10.0 Potassium bromide 0.5

Water to make one liter.

The results of these tests for speed, gamma and fog, before and afterincubation of each of the samples, are given in the following table.

Table l Concentra- Fresh Tests 1 wk. 120 F.

tion per Com- Mol of pound Silver Rela- Rela- Halide, tive Gamma Fogtive Gamma Fog gJrnol Speed Speed In Table I above, compound A isZ-carboxymethylmercapto 5 methyll-oxo-6-thiono-4,5,6,7-tetrahydro-1-thia-3,5,7-triazaindene, compound B is 5-methyl-2-methyl mercapto 4 oxo6 thiono 4,5,6,7 tetrahydro-l-thia- These 3,5,7-triazaindene, andcompound C is Z-methylamino- 4 oxo 6 thiono 4,5,6,7-tetrahydro-1-thia-3,5 ,7-triazaindene. 2 methylamino 4oxo6-thiono-4,5,6,7-tetrahydro-1-thia-3,5,7-triazaindene can also beemployed to advantage in stabilizing photographic silver halide emul-SlOHS.

Instead of incorporating the antifoggants in the photographic silverhalide emulsion, these antifoggants can be incorporated in a colloidlayer, such as a gelatin overcoating layer or interlayer, in contactwith the emulsion.

The fog-inhibiting agents which we have described can be used in variouskinds of photographic emulsions. In addition to being useful innon-sensitized emulsions, they can also be used in orthochromatic,panchromatic, and X-ray emulsions. If used with sensitizing dyes theycan be added to the emulsion before or after the dyes are added. Varioussilver halides can be used as the lightsensitive material, includingsilver bromide, silver iodide, silver chloride, silver bromiodide,silver chlorobromide, silver chlorobromiodide, etc. The antifoggants ofour invention can be used in emulsions intended for color photography,for example, emulsions containing colorforming couplers, or emulsions tobe developed by solutions containing couplers.

The polyethylene oxide polymers used in the emulsions according to ourinvention can be prepared either by polymerizing ethylene oxide in thepresence of aliphatic acids, aliphatic amines, or phenols, or byreacting the polymerized polyethylene oxide with aliphatic acids, acidchlorides, or esters, which produces similar products.

The dispersing agents can be gelatin, or other colloids, such ascollodion, albumen, cellulose derivatives, synthetic resins, etc.

What We claim as our invention and desire secured by Letters Patent ofthe United States is:

1. A photographic silver halide emulsion containing an antifoggantselected from those represented by the following general formula:

wherein R represents a member selected from the group wherein Rrepresents an alkylmercapto group containing from 1 to 3 carbon atomsand R1 represents an alkyl group of the formula C1LH21L+1 wherein n is apositive integer of from 1 to 2.

3. A photographic gelatino-silver halide emulsion containing 2carboxymethylmercapto 5 methyl 4-oxo-6-thiono-4,5,6,7-tetrahydro-l-thia-3,5,7-triazaindene.

4. A photographic silver halide emulsion containing an antifoggantselected from those represented by the following general formula:

i s S=?/ \CR M o ll 0 wherein R represents a monoalkylamino groupcontaining from 1 to 2 carbon atoms.

5. A photographic gelatino-silver halide emulsion containing2-methylamino-4-oxo-6-thiono-4,5,6,7-tetrahydro-1-thia-3,5,7-triazaindene.

6. A photographic gelatinosilver halide emulsion containing 5 methyl 2methylmercapte 4 oxo-6-thiono-4,5,6,7-tetrahydro-1-thia-3,5,7-triazaindene.

References Cited in the file of this patent UNITED STATES PATENTS2,566,659 Fry Sept. 4, 19 51

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING AN ANTIFOGGANTSELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: